EPA-A0580352 describes a tertiary lock for a thrust reverser which comprises a locking or retainer member in the form of a hook which is pivotable between a locked position in which a locking pin forming part of the thrust reverser is retained by the locking member and an open position in which the locking pin cam be removed from the locking member, thus deployment of the thrust reverser is permitted. A solenoid actuable bolt is moveable in a direction perpendicular to the axis of rotation and engageable with the locking member to prevent movement of the locking member away from its locked position other than when deployment of the thrust reverser is to take place.
The bolt is designed to transmit a significant load to part of the structure of the aircraft when movement of the locking member is to be avoided and as a result may be relatively large and heavy. The solenoid used to move the bolt must therefore be relatively powerful and as a consequence is large and heavy.